From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-0.8 required=5.0 tests=BAYES_00,INVALID_DATE
	autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 109fba,66253344eaef63db
X-Google-Attributes: gid109fba,public
X-Google-Thread: 103376,66253344eaef63db
X-Google-Attributes: gid103376,public
X-Google-Thread: 1108a1,66253344eaef63db
X-Google-Attributes: gid1108a1,public
X-Google-ArrivalTime: 1994-09-30 09:29:58 PST
Path: 
 bga.com!news.sprintlink.net!howland.reston.ans.net!EU.net!Germany.EU.net!news.dfn.de!scsing.switch.ch!swidir.switch.ch!epflnews!dinews.epfl.ch!di.epfl.ch!Magnus.Kempe
From: Magnus.Kempe@di.epfl.ch (Magnus Kempe)
Newsgroups: comp.lang.ada,comp.object,comp.lang.c++
Subject: Re: Mut. Recurs. in Ada9X w/o Breaking Encaps.?
Date: 30 Sep 1994 10:20:56 GMT
Organization: Ecole Polytechnique Federale de Lausanne
Distribution: world
Message-ID: <1994Sep30.111050@di.epfl.ch>
References: <1994Sep27.165203.9192@swlvx2.msd.ray.com>
 <36bt0c$17oo@watnews1.watson.ibm.com> <1994Sep29.103358@di.epfl.ch>
 <36eebb$jn5@disunms.epfl.ch> <CwwKwM.Cnq@inmet.camb.inmet.com>
NNTP-Posting-Host: lglsun4.epfl.ch
Mime-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Transfer-Encoding: 8bit
Keywords: Ada 9X, C++, object-oriented
Xref: bga.com comp.lang.ada:6333 comp.object:6921 comp.lang.c++:31095
Date: 1994-09-30T10:20:56+00:00
List-Id: <comp.lang.ada>

stt@spock.camb.inmet.com (Tucker Taft) writes:
: 
: The type conversion toward the end of your example is
: illegal (at least according to *our* Ada 9X front end ;-).

Damn.  Thanks.  Here's a fix, which is also accepted by GNAT :-)
Is your Ada 9X front end a program, or a human?

private
package Company.Offices.Ptrs is
  function Ptr (The_Office : Office_Reference)
    return Office_Pointer;
end Company.Offices.Ptrs;

package body Company.Offices.Ptrs is
  function Ptr (The_Office : Office_Reference)
    return Office_Pointer is
  begin
    -- here we "see" that Office is derived from Office_Parent
    return Office_Pointer (The_Office);
  end Ptr;
end Company.Offices.Ptrs;

with Company.Employees.Ptrs;
with Company.Offices.Ptrs;
package body Company.Common is
  function Office_Occupied_By (The_Employee : in Employees.Employee)
    return Offices.Office_Pointer is
  begin
    return Offices.Ptrs.Ptr (Employees.Ptrs.Office_of (The_Employee));
  end Office_Occupied_By;
  ...
end Company.Common;

: In any case, to me it is much simpler to declare abstract
: versions of Employee and Office in the same package, with appropriately
: mutually recursive (abstract) operations declared there as well.

I agree, but John Volan wanted something else...  My solution completely
avoids showing abstract and/or class-wide stuff to the client.

-- 
Magnus Kempe		"I know not what course others may take, but as for me,
Magnus.Kempe@di.epfl.ch  Give me Liberty... or give me Death!" -- Patrick Henry